The surge absorber of this kind is used for protecting, from lightning surge, electronics parts of communication equipment such as telephone sets, facsimiles, telephone exchanger plants, and modems and the like. This surge absorber is made by process that a sealing electrode is attached on both ends of a glass tube incorporating a micro-gap type surge absorbing element, the glass tube is sealed therein with inert gas such as rare gas, nitrogen gas and the like, and thereafter the glass tube, which has been heated to a high temperature by a heater such as a carbon heater, is sealed with the sealing electrode.
Generally, the sealing electrode uses metal as its member having a thermal expansion coefficient equal to that of glass in order to prevent occurrence of cracks due to thermal contraction of the glass tube at the time of sealing, and upgrades a wettability for glass at the time of sealing, thus an oxide film is provided on a surface of the, member which is a portion in contact with the glass tube. Heating the sealing electrode at a high temperature provides adhesiveness of the metal through the oxide film to the glass and the glass tube is sealed with the sealing electrode to produce air tight therein.
Conventionally, iron-nickel-chromium alloy and Dumet wire and the like have often been used for the member of the sealing electrode for soft glass. For example, Unexamined Published Japanese Patent Application No. 55-128283 discloses a surge absorber using Dumet wire as an member of a sealing electrode for sealing both ends of a soft glass tube incorporating a micro-gap type surge absorbing element. In addition, covar and iron-nickel alloy are used for hard glass or ceramics.
On the other hand, the surge absorber, in which the conventional micro-gap type surge absorbing element is incorporated in air tight in the glass tube, has no accelerating action of electron emission in the sealing electrode, accordingly an arc discharge at the time of operation passes over a conductive coating and a micro-gap on the surface of the ceramics member, but thereafter hardly reaches the sealing electrode. For this reason, a long time is required for forming an arc discharge in vicinity of the micro-gap, the conductive coating and the micro-gap are deteriorated because of the arc discharge, this then provides an adverse effect to a service life characteristic or a characteristic such as a surge resistance and the like of the surge absorber.
An object of the present invention is to provide a sealing electrode capable of sealing at a relatively lower temperature in an atmosphere of inert gas and having an electron emission accelerating action in addition to a satisfactory adhesiveness to the glass tube.
Another object of the present invention is to provide a sealing electrode capable of easily soldering lead wire.
A still another object of the present invention is to provide a surge absorber having a long service-life with a higher surge resistance capable of hardly deteriorating a conductive coating and a micro-gap at the time of sealing and arc discharging.